Benign prostatic hyperplasia (BPH) involves hyperplasia of prostatic stromal and epithelial cells, resulting in formation of large discrete nodules in the transition zone of the prostate gland. When sufficiently large, the nodules impinge on the prostatic urethra and increase resistance to flow of urine from the bladder, causing discomfort for the patient. Resistance to urine flow requires the bladder to work harder during voiding, leading to progressive hypertrophy, instability and weakness of the bladder muscle. Various treatments are available for BPH, including medication such as alpha blockers and 5-reductase inhibitors, clean intermittent self-catheterisation, surgery and minimally invasive therapies such as transurethral microwave thermotherapy and transurethral needle ablation. A further treatment option is to implant a stent within the prostatic urethra. One such stent is described in U.S. Pat. No. 5,269,802 and comprises two rings connected by three struts that maintain the two rings in a co-planar relationship. In use, the larger of the two rings is placed in the bladder and the smaller ring is placed in the prostatic urethra. Prostatic stents can offer immediate relief for symptoms of BPH but they have fallen out of favour due a high rate of side effects. They are usually long cylindrical type stents that resemble traditional stents used in in the heart blood vessels or for peripheral vascular disease. They can migrate from their deployment position and travel to the bladder or to the membranous urethra (up to 12.5% of patients), encrust and block urethra (up to 27.5%), cause incontinence (up to 3%) and pain. Cases of a profound inflammatory response to prostatic stents have been reported. In total, these combined side effects have historically resulted in 8% to 47% of prostatic stents to be removed. In addition, these previous prostatic stents have not had designs which accommodate the unique characteristics of the prostatic urethra.
WO2015/138763 describes urethral expanders configured for implantation into the prostatic urethra and in-situ expansion and comprising a number of spaced apart interconnected circular ring. This device suffers from a number of drawbacks including: increased encrustation due to the circumferential disposition of the rings meaning that they will meet the urine at 90°, difficulty in removal due to the rings being embedded at 90° to the longitudinal axis of the urethra; the rings impinging on the verumontanum which may block some of the ejaculatory and prostatic ducts; the rigidity and static nature of the ring solution impeding the natural movements of the prostatic urethra during urination and ejaculation and causing pain; and the spaced-apart nature of the rings which effects non-continuous expansion along the length of the prostatic urethra.